The Automatically Switched Optical Network (ASON) has a function of automatic discovery of network control topology and resource topology, and the function of automatic establishment, rerouting recovery or soft rerouting when in failure can therefore be implemented for Label Switched Path (LSP) of Switched Connection (SC) or Soft Permanent Connection (SPC).
If multiple instances of SC or SPC adding/deleting, rerouting or soft rerouting adjustments are performed for the ASON networking, there will be timeslot fragments on some links, which may affect the establishment of concatenated bandwidth SC or SPC. As shown in FIG. 1, there are eight timeslots between network element A and network element B in total. When created, LSP1, LSP2, LSP3, LSP 4 and LSP 5 all go through one link between network element A and network element B, and occupy timeslot 1, timeslot 2, timeslot 3 and timeslot 4, timeslot 5 and timeslot 6, respectively.
If LSP2 and LSP4 are deleted, rerouted or adjusted to other links by manual soft rerouting, timeslot 2 and timeslot 5 change to idle state as shown in FIG. 2. Then the link has four idle timeslot bandwidths including timeslot 2, timeslot 5, timeslot 7 and timeslot 8. However, there is a cavity between timeslot 2 and timeslot 5 as well as between timeslot 5 and timeslot 8, and a timeslot label of four consecutive timeslot bandwidths can not be allocated. As a result, the link resource is not available for the establishment, rerouting or soft rerouting of an LSP occupying four timeslot bandwidths. Likewise, if timeslot 7 and timeslot 8 are occupied, the link resource is not available for the establishment, rerouting or soft rerouting of an LSP occupying two timeslot bandwidths either even though there are still idle timeslots, timeslot 2 and timeslot 5.
To solve the above problem, a conventional method of adjusting timeslot fragments is described below. The timeslot fragment rate can be calculated for a link by a timeslot fragment calculator using an algorithm (e.g. a Mobipack defragmentation algorithm as described for example in S. Acharya, et al., MobiPack: Optimal Hitless SONET Defragmentation in Near-Optimal Cost, INFOCOM 2004, IEEE, Jul. 11, 2004, pp. 1819-1829, which is hereby incorporated by reference in its entirety herein), taking into account minimal moving times, the fragment granularity that can be contained and whether timeslots are unable to be randomly moved because of a certain particularity. A timeslot selector finds an optimal candidate timeslot capable of reducing the timeslot fragment rate of an optical interface. A circuit connection adjustor adjusts a service connection occupying a certain timeslot to the optimal candidate timeslot in a bridge-like manner; and during the adjustment, the service connection may suffer from transient disruption (several milliseconds generally). For example, LSP5 can be adjusted from timeslot 6 to timeslot 2 as shown in FIG. 2, and the timeslots after adjusted are shown in FIG. 3.
During the implementation of the present invention, the inventors discovered the following problems in the above conventional method.
The conventional method only takes the timeslot fragment adjustment for a single link into account. If the timeslot fragment adjustment is performed for multiple links, or for all links of a network, the timeslot fragment adjustment will be performed for each link respectively. Therefore, the service connection going through multiple links may repeatedly suffer from multiple occurrences of transient disruption. In addition, during the timeslot fragment adjustment for these links, their resource usage and the maintenance of a service connection going through the links would be inevitably affected. If the conventional method of adjusting timeslot fragments is applied to the adjustments shown in FIG. 5, when the timeslot fragment adjustment is performed on the links respectively between network element A and network element B, between network element B and network element C as well as between network element C and network element D, LSP5 is adjusted from timeslot 6 to timeslot 2 on the link between network element A and network element B, from timeslot 3 to timeslot 2 on the link between network element B and network element C, and from timeslot 7 to timeslot 2 on the link between network element C and network element D. During each adjustment, LSP5 will suffer from transient disruption once, and three times in total. When the timeslot fragment adjustment is performed on the links between network element B and network element C as well as between network element C and network element D, LSP3 is adjusted from timeslot 5 to timeslot 3, and suffers from transient disruption twice. In general, the more the links are, the more occurrences of transient disruption the LSP suffers from during the adjustment, and the more the service carried by the LSP is affected.